1. Field of the Invention
The present invention relates to an optical device which can periodically or sequentially vary an optical property of the optical device, such as the focal length of a lens, the deflection angle of a prism, the divergence angle of a lenticular lens and so on.
Further, the present invention relates to a three-dimensional display device and its driving method. More specifically, the present invention relates to a technology effectively applicable to an apparatus for displaying a two-dimensional image to be displayed on a two-dimensional display device in a three-dimensional fashion.
2. Description of the Related Art
Most of the conventional optical devices are passive optical devices. The kinds of active optical devices whose optical properties can be varied by voltage or the like are quite limited. Amongst them, as an optical device employing a material having a variable refractive index, there is a liquid crystal lens disclosed in Science Research Expenditure Subsidy Research Results Report No. 59850048 (1984).
FIG. 1 shows the construction of such a liquid crystal lens. The liquid crystal lens having optical properties to be varied by voltage or the like shown in FIG. 1 is constructed with a planar convex lens 1 formed of a polymer, glass or the like, a transparent electrode formed on the surface of the planar concave lens 1, an alignment layer formed of a polyimide or the like on the transparent electrode 2, a liquid crystal 4 (ordinary nematic liquid crystal having an anisotropy of its dielectric constant which is not reversed by difference of frequency), an opposite substrate 5 opposite to these components, a transparent electrode 6 formed on the opposite substrate 5, an alignment layer 7 formed of polyimide or the like on the transparent electrode 6, and a driving device for driving these components. Here, the alignment layers 3 and 7 are in a homogeneous alignment condition for aligning the liquid crystal 4 substantially in parallel.
In the condition where no voltage is applied between the transparent electrodes 2 and 6, the liquid crystal 4 is aligned to be substantially parallel to the alignment layers 3 and 7 by the action of the alignment layers 3 and 7. In this case, an incident light beam 11 that is polarized parallel to the alignment direction is subject to an extraordinary refractive index of the liquid crystal 4. Thus, for example, the liquid crystal 4 appears to have a large refractive index in comparison with the planar concave lens 1 so that the entire optical device serves as a planar convex lens to cause convergence as an output light beam 12.
On the other hand, in the condition where an appropriate voltage is applied between the transparent electrodes 2 and 6, the liquid crystal 4 is aligned to be perpendicular to the electrode 2 and 6. In this case, the incident light beam 11 is subject to the ordinary refraction of the liquid crystal 4. Therefore, for example, the liquid crystal 4 appears to have substantially the same refractive index as the planar concave lens. Then, the entire optical device merely serves as glass plate to output a light beam 13 having substantially the same direction as the incident light beam 11.
Even in such a conventional optical device, it has been possible to sequentially vary an optical property, e.g. focal length, of the planar convex lens depending upon an applied voltage. One example of this relationship is illustrated in FIG. 2.
However, the conventional optical device has the following detects. Alignment of the liquid crystal 4 in the condition where no voltage is applied, is performed only by an anchoring force of the alignment layers 3 and 7. In such a optical device, since the liquid crystal 4 has a large thickness of several hundreds xcexcm or more, a drawback has been encountered in that a resumption timing upon driving is delayed significantly by several seconds, as shown in FIG. 3. Furthermore, even if the applied voltage is increased, the resumption timing can be hardly improved. Therefore, currently, there is no effective method for shortening a resumption period.
As set forth above, when the liquid crystal 4 is aligned only by the anchoring force of the alignment layers 3 and 7, molecules 4a of the liquid crystal 4 may be aligned along a curved surface of the planer concave lens in a portion located in the vicinity of the transparent electrode 2, as shown in FIG. 4. Therefore, alignment of a part of the liquid crystal tends to be inclined, so that the refractive index to be sensed by the incident light beam becomes closer to the refractive index of the planar concave lens, thereby making the amount of variation of the optical property smaller. Furthermore, there is a disadvantage in that distribution of the variation amount of the optical property depends on the position with respect to the lens.
Further, since the transparent electrode 2 is formed on the surface of the planar concave lens 1, when the voltage is applied, an electric field perpendicular to its surface is established in the vicinity of the transparent electrode 2 so that the liquid crystal 4 may be aligned perpendicularly to the surface thereof. As a result, there arises an inclination of the alignment of a part of the liquid crystal 4 to form a region where the refractive index sensed by the incident light beam is significantly different from the refractive index of the planar concave lens 1. Thus, the incident light beam which should pass through without any deflection substantially, is locally deflected.
Furthermore, in the case where the surface configuration of the planar concave lens 1 is more complicated, particularly when it has deep grooves or sharp projections, it becomes difficult to uniformly form the transparent electrode, so that a circuit breakage or high resistance is liable to occur.
Additionally, in such case, an alignment process of the alignment layers for aligning the liquid crystal, such as a rubbing process and the like, becomes difficult. Further, the distance between the transparent electrodes varies at different positions as is clear from FIG. 1. Despite this fact, since an equal voltage is applied to all positions of the transparent electrodes, degradation of insulation, short circuits, etc. are liable to occur in a narrow region.
As set forth above, the conventional active optical device employing a material having a variable refractive index encounters various practical drawbacks or shortcoming in production and driving.
It is an object of the present invention to provide an optical device which can be driven at high speed, achieves high uniformity, is easy to fabricate, and can vary an optical property sequentially, periodically in an active manner.
According to the present invention, there is an optical device comprising:
a transparent material layer having a desired curved surface configuration;
a layer including a variable refractive index material having a dielectric constant anisotropy and having a property in which a sign of a difference xcex94∈ in dielectric constant due to the anisotropy is reversed at driving frequencies f1 and f2;
at least two transparent electrodes arranged to sandwich the transparent material layer and the layer including the variable refractive index material; and a driving device supplying a voltage including the driving frequencies f1 and f2 between the transparent electrodes.
The optical device according to the invention enables high speed operation by varying the refractive index by varying the frequency of a voltage which is applied to the variable refractive index material in order to vary an optical property of the device. Furthermore, since the force of the electric field can be always used, the speed can be made higher by increasing the electric field.
In addition, in the optical device according to the invention, the force of the electric field can be varied by the variable refractive index material, and since the transparent electrodes are not provided on the side of the variable refractive index material of the transparent material layer, the optical device is hardly influenced by the surface configuration of the transparent material layer, compared to the prior art device, regardless of the condition of the variable refractive index material. Therefore the amount of variation of the optical property can be easily made uniform. Since the transparent electrodes are not provided on the side of the variable refractive index material of the transparent material layer in the optical device according to the present invention, it becomes unnecessary to form a film to meet the shape of a complicated surface configuration to facilitate fabrication of the optical device, compared to the prior art device. Furthermore, since the transparent electrodes are not provided on the side of the variable refractive index material of the transparent material layer, the distance between the transparent electrodes can be maintained substantially the same, and the transparent material layer is always present between the transparent electrodes, degradation of insulation, shorts, and so on hardly occur.
Further, by replacing one of the transparent electrodes with an electrode reflecting at least a part of the incident light beam, an active mirror, half mirror or various other types of optical devices for varying an optical property can be realized.
According to the present invention, there is an optical device comprising:
a layer including a variable refractive index material having dielectric constant anisotropy and having a property to reverse signs of a difference of dielectric constant xcex94∈ due to anisotropy at driving frequencies f1 and f2;
at least two transparent electrodes arranged to sandwich the layer including the variable refractive index material; and
a driving device applying a voltage, in which voltages from V1 to VN respectively having respective primary frequencies f1 to fN (Nxe2x89xa72) are superimposed, between the transparent electrodes.
According to the present invention, there is an optical device comprising:
a layer of transparent material having a desired curved surface configuration;
a layer including a variable refractive index material having a positive or negative dielectric constant anisotropy;
at least two transparent electrodes arranged to sandwich the layer of the transparent material and the layer including the variable refractive index material; and a driving device for always supplying a voltage substantially equal to or greater than an amplitude
of a voltage establishing static and vertical alignment in the variable refractive index material.
As set forth above, the optical device according to the present invention has a driving device which can always supply the voltage having an amplitude equal to or greater than the voltage, at which the variable refractive index material is statistically aligned to generate electrofluid motion in the molecules of the liquid crystal to change the refractive index of the variable refractive index material in such a way that the orientation of the liquid crystal molecules vary in synchronism with a frequency twice that of the frequency of the voltage applied, between the state where the orientation of the liquid crystal molecules is perpendicular or parallel to the electrode and the state where the orientation of the liquid crystal molecules is slightly inclined from the former state. Therefore, the optical device according to the present invention can vary the optical property at a high speed, sequentially, periodically and uniformly. Furthermore, it becomes unnecessary to process the film to meet a complicated surface configuration, and the fabrication can be facilitated.
According to the present invention, there is a three-dimensional display device for forming a three-dimensional image from two-dimensional images on a display portion, comprising:
a layer of a transparent material having a desired curved surface configuration;
a layer of a variable refractive index material having a refractive index varying in accordance with a voltage applied thereto;
at least two transparent electrodes arranged to sandwich the layer of the transparent material and the layer including the variable refractive index material;
an imaging position shifting portion for shifting an imaging position of the two-dimensional image displayed on the display portion;
a synchronizing portion for synchronizing an updating period of the two-dimensional image displayed on the display portion with a shifting period of the imaging point of the imaging position shifting portion; and
a driving portion for driving the imaging point shifting portion by applying a voltage to the at least two transparent electrodes in accordance with an output from the synchronizing portion.
The three-dimensional display device according to the present invention decomposes the three-dimensional image into two-dimensional images (depth sample images) belonging to planes set at a predetermined interval in a depth direction of an image pick-up position for displaying the images in a predetermined sequence on the display portion, and the imaging position of the image to be displayed on the display portion is varied by the imaging portion shifting portion. Here, the image displayed on the display portion and the imaging position are synchronized by the synchronizing portion so that the observer may view the image displayed on the display portion as a three-dimensional image.
According to the present invention, there is a driving method of driving a three-dimensional display device including a display portion for displaying two-dimensional images, an imaging point shifting portion disposed between the display portion and an observer, a synchronizing portion for synchronizing an updating period of the two-dimensional images displayed on the display portion with a shifting period of the imaging point of the imaging point shifting portion, and a driving portion for driving the imaging point shifting portion, the a driving method comprising the steps of:
outputting a plurality of driving signals of an output voltage VN (Nxe2x89xa72) having frequency fN as a primary frequency for a predetermined period of time assigned to each of the driving signals in a predetermined sequence to drive the imaging point shifting portion in the driving portion; and
updating and displaying the two-dimensional images in a predetermined sequence on the display portion in the synchronizing portion.
According to the present invention, there is a driving method of driving a three-dimensional display device including a display portion for displaying two-dimensional images, an imaging point shifting portion disposed between the display portion and an observer, a synchronizing portion for synchronizing an updating period of the two-dimensional images displayed on the display portion with a shifting period of the imaging point of the imaging point shifting portion, and a driving portion for driving the imaging point shifting portion, the a driving method comprising the steps of:
in the driving portion:
generating a driving signal of a predetermined output voltage in which a frequency fN (Nxe2x89xa72) is superimposed;
applying the driving signal to the imaging position shifting portion;
varying the output voltage in a predetermined sequence in accordance with a synchronization signal of the synchronizing portion; and
in the synchronization portion:
outputting a synchronization signal in the synchronization portion when updating two-dimensional images to be displayed on the display portion.
In the foregoing three-dimensional display device, there appears a phantom image of the image on the back side or inside which should be hidden. Therefore, it can be useful only for reproducing a wire frame like three-dimensional image, in practice. The invention makes it possible to display the real three-dimensional image display in this case.
According to the present invention, there is a three-dimensional display device comprising:
a phantom three-dimensional display device for displaying a phantom three-dimensional image; and
a shutter device formed by a shutter element for controlling a light transmittance, the shutter device being located at a position where the phantom three-dimensional image is reproduced or a position optically equivalent to the position. According to the three-dimensional display device, the shutter element of the shutter device, interputs the incident light beam or scatters the light beam while the phantom image on the back side as viewed from the observer is being reproduced. By this display device, many of the visual cues to depth perception can be satisfied and the natural three-dimensional image with no phantom phenomenon can be reproduced in the form of motion picture.
According to the present invention, there is a three-dimensional display device comprising:
a phantom three-dimensional display device for displaying a phantom three-dimensional image; and
a shutter device formed by a shutter element for controlling a light transmittance, the phantom three-dimensional image being a real image, and the shutter element being a photoreactive element for lowering a light transmittance in a real image region at the position of the shutter element in accordance with an imaging light beam of the real image.
According to the present invention, there is a head-mount display device comprising:
two display devices corresponding to left and right eyes and each including a two-dimensional display device and an optical device having a variable focal length; and
a control device for controlling the two-dimensional display device and the optical device having a variable focal length,
the display devices being mounted to left and right eyes, and the control device synchronously driving the two-dimensional display device and the optical device to perform three-dimensional display.
The head-mount display device according to the present invention is worn on respective left and right eyes of a human being so that the human being or viewer can view display images on the two-dimensional display devices through the optical device of variable focal length. Then, by varying the focal length of the optical device, the virtual image position of the display image of the two-dimensional display device is varied in the depth direction. According to this display device, visual cues to depth perception, such as binocular disparity, convergence, and focus of the eyes in stereoscopy can be satisfied with no discrepancy and the natural three-dimensional image with no phantom phenomenon can be reproduced at a high speed.